Uses Ascii variants of LoadLibrary,Get/SetEnvironmentVariable_A_
and adds a freeError function
includes windows.h instead of pre/postwin.h

Change-Id: I88b7e3ed3818078efec5688e207da47dc4049b98
Reviewed-on: https://gerrit.libreoffice.org/21600Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Oliver Specht <oliver.specht@cib.de>